This invention broadly relates to a substrate with a multilayer film, a reflection type mask blank, and a reflection type mask for use in a semiconductor production to control a light ray, and a production method thereof as well as a method for manufacturing a semiconductor device.
Herein, it should be noted that an EUV (Extreme Ultra Violet) light ray, which will be described later, represents a light ray with wavelength band of a soft X-ray region or a vacuum ultraviolet region, more specifically a light ray with wavelength of about 0.2-100 nm.
Conventionally, use has been made of a photolithography method using a visible light ray or an ultraviolet light ray as a transfer technique of a fine pattern required for forming an integrated circuit with fine patterns on a Si substrate or the like in a semiconductor industry.
However, a semiconductor device has been rapidly reduced in size in recent years. Consequently, shortening wavelength has been largely restricted because of an exposure limit in conventional optical exposure.
Under such a circumstance, a resolution limit of a pattern will be a half of exposure wavelength in case of the optical exposure. It is predicted that the resolution limit is equal to approximately 70 nm even if an F2 laser ray (157 nm) is used.
Therefore, a great attention has been paid for an EUV lithography (hereinafter, it will be abbreviated as xe2x80x9cEUVLxe2x80x9d) as an exposure technique, in which an EUV light ray (13 nm) having wavelength shorter than the F2 laser ray is used, as a next generation exposure technique with 70 nm or shorter.
In general, an image forming principle of EUVL is the same as the photolithography. However, absorption rate for all substances with respect to the EUV light ray is high, and further, index of refraction is substantially equal to 1.
In consequence, a refraction optical system can not be used different from the optical exposure, and alternatively, a reflection optical system must be used.
In this event, suggestion has been made about a transmission type mask using a membrane as a mask used in the above-mentioned case. However, the absorption rate of the membrane for the EUV light ray becomes high. Thereby, exposure duration becomes long, and a desired throughput can not be maintained. For this reason, the reflection type mask for exposure is generally used in the recent years.
For example, a reflection type mask for exposure is disclosed in Japanese Examined patent publication No. 7-27198 and Japanese Unexamined Patent Publication No. 8-213303. In such a reflection type mask, a reflection layer with a multilayer structure is formed on a substrate and an absorber for absorbing a soft X-ray or a vacuum ultraviolet ray is formed to a pattern shape on the reflection layer.
FIGS. 1A and 1B are schematic views showing an example of the conventional reflection type mask blank for exposure and the conventional reflection type mask for exposure.
As illustrated in FIG. 1A, a reflection film 22 with a multilayer structure is deposited on a substrate 21, an etching stopper layer 23 is deposited on the reflection film 22, and an absorber layer 24 is deposited on the etching stopper layer 23.
With such a structure, a pattern is formed for the absorber layer 24 of the reflection type mask blank for exposure, and an unnecessary etching stopper layer 23 on the multilayer film is removed, thus manufacturing the reflection type mask for exposure illustrated in FIG. 1B.
Under this circumstance, the soft X-rays entered to the reflection type mask for exposure is reflected by the reflection film 22, and is absorbed at a portion, in which the pattern of the absorber 24 is formed, without reflection. As a result, the pattern can be formed with high contrast between a reflection portion and an absorption portion.
However, it is necessary to increase film density of each layer of the multilayer film 22 to obtain high index of reflection in the reflection type mask for exposure in which the multilayer film 22 is deposited on the above-mentioned substrate 21. Consequently, the multilayer film 22 inevitably has high compression stress.
In the cause of such high compression stress, the substrate 21 is largely warped or deformed through a convex surface, as illustrated in FIG. 2. As a result, warping also occurs for the surface of the multilayer film 22 serving as a reflection surface of the EUV light ray.
For example, when the compression stress of about 200 MPa is applied for the multilayer film 22 with a 0.3 xcexcm thickness on a quartz substrate having a 6 inch square and a 6.35 mm thickness, warping (deformation) on the order of 500 nm inevitably takes place for an area of 140xc3x97140 mm.
As discussed above, transfer accuracy is lowered or image placement error occurs in the cause of the warping of the surface of the multilayer film 22 during transferring a pattern onto a wafer according to the conventional technique. Thereby, transfer can not be carried out with high accuracy. To solve such a problem, the stress of the multilayer film 22 may be reduced. However, this method is not preferable from a practical viewpoint because the film density and the reflectivity of the EUV light ray are lowered.
Further, the warping of the multilayer film 22 is affected by the warping inherent to the substrate 21 in addition to the deformation of the substrate 21 due to the compression stress of the above-mentioned multilayer film 22.
Accordingly, it is difficult to effectively correct the warping of the surface of the multilayer film 22 by merely reducing the stress of the multilayer film 22.
This invention is made under the above-discussed background. It is therefore an object of this invention to provide a substrate with a multilayer film, a reflection type mask blank for exposure, and a reflection type mask for exposure which has a surface of a multilayer film with high flatness by correcting warping (deformation) of the surface of the multilayer film formed by stress of the multilayer film and the warping (deformation) of the substrate itself.
According to a first aspect of this invention, a reflection type mask blank for EUV exposure has a substrate.
Further, a multilayer film is formed on the substrate so as to reflect an EUV light ray. An absorber layer is formed on the multilayer film so as to absorb the EUV light ray. Under this circumstance, the multilayer film has flatness with respect to a surface thereof, and the flatness is 100 nm or less.
Herein, the flatness described in the instance specification indicates the warping (deformation quantity) of the surface represented by TIR (Total Indicated Reading), and will be defined as follows.
Namely, a plane surface defined by a least square method based upon a substrate surface 31 is defined as a focal plane in FIG. 3. Subsequently, an absolute value of a difference between a highest position A of the substrate surface 31 over the focal plane 32 based upon the focal plane 32 and a lowest position B of the substrate surface 31 under the focal plane 32 is defined as the flatness. Therefore, the flatness is always a positive number.
In this event, a measured value within a area of 140xc3x97140 mm is defined as the flatness according to this invention. For example, it is a measured value within the area of 140 xc3x97140 mm with respect to a center of a 6 inch substrate.
According to a second aspect of this invention, a reflection type mask blank for EUV exposure has a substrate.
Further, a multilayer film is formed on the substrate so as to reflect an EUV light ray. A light absorber layer is formed on the multilayer film so as to absorb the EUV light ray. A stress correction film corrects warping of a surface of the multilayer film. In this event, the warping is formed by warping of the substrate and stress of the multilayer film.
According to a third aspect of this invention, the stress correction film has tensile stress, and is placed between the substrate and the multilayer film in the mask blank of the second aspect of this invention.
According to a fourth aspect of this invention, the stress correction film has compressive stress, and is placed on a back surface of the substrate in the mask blank of the second aspect of this invention.
According to a fifth aspect of this invention, the stress correction film is made of material containing Ta in the mask blank as claimed in any one of the second through fourth aspects of this invention.
According to a sixth aspect of this invention, the stress correction film is made of material containing Ta as a major component and at least B in the mask blank of the fifth aspect of this invention.
According to a seventh aspect of this invention, a reflection type mask for EUV exposure is produced by using the reflection type mask for EUV exposure blank of any one of the first through sixth aspects of this invention.
According to an eighth aspect of this invention, a reflection type mask for EUV exposure produced by using the reflection type mask for EUV exposure blank of any one of the first through sixth aspect of this invention is manufactured.
According to a ninth aspect of this invention, a semiconductor device is manufactured such that a pattern is transferred on the substrate by using the reflection type mask for EUV exposure of the seventh aspect of this invention.
According to a tenth aspect of this invention, a substrate has a multilayer film for reflecting an EUV light ray onto a substrate. Under such a condition, the multilayer film has flatness with respect to a surface thereof, and the flatness is 100 nm or less.
According to an eleventh aspect of this invention, a substrate has a multilayer film for reflecting an EUV light ray onto a substrate.
Further, a stress correction film corrects warping of a surface of the multilayer film. In this case, the warping is formed by warping of the substrate and stress of the multilayer film.
According to a twelfth aspect of this invention, an EUV reflection mirror is produced by using the substrate with the multilayer film of the tenth or eleventh aspect of this invention.
According to a thirteenth aspect of this invention, a reflection type mask blank for exposure has a substrate.
Further, a multilayer film is formed on the substrate so as to reflect a light ray. A light absorber layer is formed on the multilayer film so as to absorb the light ray.
Under this circumstance, the multilayer film has flatness with respect to a surface thereof, and the flatness is 100 nm or less.
According to a fourteenth aspect of this invention, a reflection type mask blank for exposure has a substrate.
Further, a multilayer film is formed on the substrate so as to reflect a light ray. A light absorber layer is formed on the multilayer film so as to absorb the light ray. A stress correction film corrects warping generated on a surface of the multilayer film when the stress correction film is not formed.
According to a fifteenth aspect of this invention, a reflection type mask for exposure is produced by using the reflection type mask blank for exposure of the thirteenth or fourteenth aspect of this invention.